1. Field of the Invention
The present invention relates to a pump enable system and method; and more particularly, a pump enable system and method for variable-displacement piston pumps.
2. Description of Related Art
FIG. 1 schematically illustrates a well-known variable-displacement piston pump 10 such as Vickers Incorporated's Model No. PVE19R930CVPC. The piston pump 10 includes a pump 12 having a plurality of pistons (not shown). The pump 12 is connected between a suction line 14 and a pressure line 16, and is driven by an engine 18. Oil leaking in the pump 12 is drained via a drain line 20.
As is well-known, a swash plate 22 (also known as a wobble plate), connected to the pistons in the pump 12, controls the displacement of the pistons; and thus, the flow rate of the pump 12. More specifically, the position of the swash plate 22 determines the displacement of the pistons in the pump 12. A servo piston 24 controls the movement of the swash plate 22 based on hydraulic pressure (i.e., fluid) supplied thereto.
As shown in FIG. 1, a pressure compensation valve 26 and a flow compensation valve 28 cooperatively regulate the supply of hydraulic pressure generated by the pump 12 to the servo piston 24 based on the hydraulic pressure in a load sense line 30. The load sense line 30, for instance, is connected to a directional control valve (not shown), which when placed in a state requiring hydraulic pressure supplies hydraulic pressure to the load sense line 30. Both the pressure and flow compensation valves 26 and 28 are two-state valves.
When a load is placed on the pump 12, the pressure compensation valve 26 and the flow compensation valve 28 are both placed in a first state as shown in FIG. 1. In this first state, the hydraulic pressure generated by the pump 12 is not supplied to the servo piston 24, and the servo piston 24 is connected with the drain line 20 to remove hydraulic pressure therefrom. As a result, the servo piston 24 retracts and the swash plate 22 moves to an inclined position, which increases the displacement of the pistons in the pump 12 and increases the flow rate of the pump 12.
When no load is placed on the pump 12, the pressure compensation valve 26 and the flow compensation valve 28 both attain a second state. While not shown as being in the second state, FIG. 1 does illustrate the second states of the pressure and flow compensation valves 26 and 28. In this second state, the hydraulic pressure generated by the pump 12 is supplied to the servo piston 24. As a result, the servo piston 24 extends and moves the swash plate 22 to a more vertical position, which reduces the piston displacement in the pump 12 and decreases the flow rate of the piston pump 12. When fully stroked, the servo piston 24 moves the swash plate 22 to a position which reduces the hydraulic pressure generated by the pump 12 to a stand-by pressure.
Whether the pressure and flow compensation valves 26 and 28 are placed in the first or second state depends on the hydraulic pressure in the load sense line 30 and the pressure line 16. Namely, the hydraulic pressure generated by pump 12 is supplied to first control inputs 40 and 44 of the pressure compensation valve 26 and the flow compensation valve 28, respectively, and the hydraulic pressure in the load sense line 30 is supplied to a second control input 42 of the pressure compensation valve 26. First and second springs 45 and 46 bias the pressure and flow compensation valves 26 and 28, respectively, to the right in FIG. 1.
When no load is placed on the load sense line 30, the hydraulic pressure generated by the pump 12 causes the pressure and flow compensation valves 26 and 28 to move to the left in FIG. 1 (i.e., the second state). However, when a load is placed on the load sense line 30, the hydraulic pressure applied to the second control input 42 of the pressure compensation valve 26 causes the pressure compensation valve 26 to move to the right (i.e., the first state). As a result, the hydraulic pressure applied to the first control input 44 of the flow compensation valve 28 is exhausted to the drain line 20 via the pressure compensation valve 26, and the flow compensation valve 28 moves to the right (i.e., the first state).
The hydraulic pressure generated by the pump 12 and supplied via the pressure line 16 typically powers hydraulically operated machinery. As discussed above, the variable-displacement piston pumps 10 can be connected to a directional control valve. The directional control valve applies hydraulic pressure to the load sense line 30 depending on the need for hydraulic pressure from the variable-displacement piston pump 10. Unfortunately, if the directional control valve sticks in an open state for operating machinery connected thereto when an operator wants the directional control valve closed, the variable-displacement piston pump 10 continues to supply hydraulic pressure.
As such, it is desirable, such as in emergency conditions, to immediately stop operation of that machinery. Often this is accomplished by removing the supply of hydraulic pressure necessary to operate the machinery. FIG. 1 illustrates a conventional dump system for removing the supply of hydraulic pressure.
As shown in FIG. 1, a dump valve 32 is connected between the pressure line 16 and a reservoir 34. In a closed state, the dump valve 32 prevents hydraulic pressure from flowing to the reservoir 34 from the pressure line 16. However, in an open state, as shown in FIG. 1, the dump valve 32 permits hydraulic pressure to flow to the reservoir 34, which substantially eliminates hydraulic pressure in the pressure line 16. By placing the dump valve 32 in the open state, operation of machinery utilizing the hydraulic pressure in the pressure line 16 can be brought to a halt.
FIG. 2 schematically illustrates another well-known variable-displacement piston pump 110 such as Parker Hannifin Corporations Model No. PAVC65X29948. The piston pump 110 includes a pump 112 having a plurality of pistons (not shown). The pump 112 is connected between a suction line 114 and a pressure line 116, and is driven by an engine 118. Oil leaking in the pump 112 is drained via a drain line 120.
As is well-known, a swash plate 122, connected to the pistons in the pump 112, controls the displacement of the pistons; and thus, the flow rate of the pump 112. More specifically, the position of the swash plate 122 determines the displacement of the pistons in the pump 112. A servo piston 124 controls the movement of the swash plate 122 based on hydraulic pressure (i.e., fluid) supplied thereto.
As shown in FIG. 2, a differential adjustment valve 126 regulates the supply of hydraulic pressure generated by the pump 112 to the servo piston 124 based on the hydraulic pressure in a load sense line 130. The load sense line 130, for instance, is connected to a directional control valve (not shown), which when placed in a state requiring hydraulic pressure supplies hydraulic pressure to the load sense line 130.
The differential adjustment valve 126 is a two-state valve. When no load is placed on the pump 110, the differential adjustment valve 126 is placed in a first state. While FIG. 2 does not illustrate the differential adjustment valve 126 in the first state, FIG. 2 does illustrate the first state. Specifically, because no hydraulic pressure is supplied to the control input 140 of the differential adjustment valve 126 by the load sense line 130, a spring 142 biases the differential adjustment valve 126 down in FIG. 2 (i.e., biases the differential adjustment valve 126 towards the first state). This connects the servo piston 124 to the drain line 120, and hydraulic pressure at the servo piston 124 exhausts via the drain line 120. As a result, the servo piston 124 retracts and moves the swash plate 122 to a more vertical position, which reduces the piston displacement in the pump 112 and decreases the flow rate of the pump 112. When fully retracted, the servo piston 124 moves the swash plate 122 to a position which reduces the hydraulic pressure generated by the pump 112 to a stand-by pressure.
When a load is placed on the pump 110, the differential adjustment valve 126 is placed in a second state as shown in FIG. 2. Namely, when a load is placed on the pump 110, hydraulic pressure is applied to the control input 142 of the differential adjustment valve 126 by the load sense line 130. This hydraulic pressure causes the differential adjustment valve 126 to move up in FIG. 2 (i.e., move towards the second state). In this second state, the pressure line 116 is connected to the servo piston 124, and hydraulic pressure is supplied to the servo piston 124. As a result, the servo piston 124 extends and the swash plate 122 moves to an inclined position, which increases the displacement of the pistons in the pump 112 and increases the flow rate of the pump 112.
The hydraulic pressure generated by the pump 112 and supplied via the pressure line 116 typically powers hydraulically operated machinery in the same manner discussed above with respect to the variable-displacement piston pump 10 of FIG. 1. As such it is desirable, such as in emergency conditions, to immediately stop operation of that machinery
As shown in FIG. 2, a dump valve 132 is connected between the pressure line 116 and a reservoir 134. In a closed state, the dump valve 132 prevents hydraulic pressure from flowing to the reservoir 134 from the pressure line 116. However, in an open state, as shown in FIG. 2, the dump valve 132 permits hydraulic pressure to flow to the reservoir 134, which substantially eliminates hydraulic pressure in the pressure line 116. By placing the dump valve 132 in the open state, operation of machinery utilizing the hydraulic pressure in the pressure line 116 can be brought to a halt.
In the dump systems of FIGS. 1 and 2, the immediate elimination of hydraulic pressure in the pressure line 116 causes a significant shock or jolt. Furthermore, this immediate elimination of hydraulic pressure defeats the benefits provided by systems incorporating a ramp down feature. Systems incorporating a ramp down feature include hydraulic elements which gradually reduce their demand for hydraulic pressure such that the hydraulic pressure supplied by the variable-displacement piston pump 10 or 110, in response to this demand, gradually decreases. Consequently, machinery operating based on the hydraulic pressure supplied by the variable-displacement piston pump 10 or 110 gradually comes to a halt.